The present invention relates generally to apparatus for cutting gears and, more particularly, to apparatus for cutting arcuately-shaped worms.
A worm gear is a gear generally including a worm and a worm wheel, and is usually employed to connect nonparallel, nonintersecting, perpendicular shafts. Most often, the worm is the driving gear and the worm wheel is the driven gear. The worm has a shank around which at least one complete tooth is helically formed. In many applications, the outer contour of the shank and the tooth is constructed so as to generally conform with the gear face of the wheel which it drives. For instance, a worm may be barrel-shaped (i.e., convexly curved) so that it meshes with an internal ring gear, the radius of curvature of the respective gear faces being similar to increase the contact area therebetween; or it may be hourglass-shaped (concavely curved) to mesh with an externally toothed gear.
Manufacturing such an arcuately-shaped worm may present substantial difficulties since the worm blank must simultaneously be rotated about the worm axis and be moved axially and arcuately relative to the gear cutter, all at predetermined fixed rates. The apparatus here is intended to cut such arcuately-shaped worms. Although the apparatus is primarily intended to cut worms with a relatively large pitch diameter and of relatively short length having few revolutions of the tooth about the shank, it need not be so limited.
Schurr U.S. Pat. No. 1,960,460 discloses a device for rotating the worm blank on the worm axis and simultaneously moving the cutter arcuately along the blank at a speed proportional to the rate of rotation of the gear blank. Schurr provides a means for producing a worm with a true helix configuration. However, when forming worms having large diameter and with a land that makes few turns, there is no need to provide compensatory complex motion so that the worm tooth or groove has a constant profile or encircles the shank in a true helix. Schurr et al U.S. Pat. No. 1,243,767 shows an apparatus employing a plurality of cutting elements revolving into cutting engagement with a rotating gear blank. Trbojevich U.S. Pat. No. 2,011,956 suggests a method of cutting a globoid worm, but offers no apparatus for conveniently carrying out that method. Therein, the suggestion is to arcuately translate the worm blank relative to the cutter as it is rotated. Graves U.S. Pat. No. 2,126,990 shows a method for properly applying a cutting tool to the worm blank to finish the thread of a globoid worm.